Scan doubling, was Re: looking for a book on monitor theory

Chris M chrism3667 at
Mon Sep 19 20:42:40 CDT 2005

> > I'll echo that I don't think it's practical to do
> this.  Modern multisync CRT monitors contain lots of
> circuitry to manage the various linearity and
> distortion problem imposed by the need to vary sweep
> frequencies.  The horizontal sweep components, in
> particular, won't let you get much below 32 Khz or
> so.   

 I'm sure you have a better handle on this then I do,
but they're built not to go below ~32khz these days,
because there's no reason to. The earlier multisyncs
went down to 15.75khz. I wasn't suggesting it wouldn't
be a sizeable job. Might not be practical, who knows.
It would just be nice to have a way of producing an
output from a vintage puter in the absence of anything
older, and larger (19"+). 

> > I suppose one could use a TV-freqency video "frame
> grabber" on a PC to acquire then display on a modern
> monitor, but that seems to be the long way around
> the job.

 That's actually an interesting suggestion, but I'm
not generally looking to grab interlaced stuph at tv
frequencies. Still it might be easier to modify
something like that then modifying the monitor itself
(?). To sync down to cga frequencies would be nice,
but generally the puters/cards I'm looking to work
with are around the 25khz area.
 Princeton used to sell an item called a scan doubler.
It allowed the use of a 400 line non-interlaced
monitor with a cga frequency card, in effect doubling
(almost) the horizontal sync rate (I guess the
overscan wasn't doubled, so 15.75khz became about
24-25 khz, not 31.5khz). Information of something like
that (I can't find one) would be appreciated. There
were similar things for the Amiga IIRC, but maybe
those were just "flicker fixers", and only took it's
interlaced video and changed it into non-interlaced

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